Rubber vulcanization agents of sulfur and olefin

ABSTRACT

Superior vulcanization agents for rubber are prepared by reacting sulfur with an olefin at 140°-160° C. in an aqueous reaction media in the presence of a basic catalyst and a dispersing agent.

This is a divisional of application Ser. No. 896,688, filed on Aug. 15,1986, now U.S. Pat. No. 4,739,036.

TECHNICAL FIELD

This invention relates to vulcanization agents for rubber and a novelmethod for their preparation. The invention also relates to vulcanizateswhich comprise a major portion of rubber and a minor proportion of thematerial prepared in accordance with this invention. More particularly,the invention concerns a novel process for the preparation of a usefulrubber curing agent which will provide a rubber having improved physicalproperties.

BACKGROUND ART

Obtaining a uniform dispersion of elemental sulfur in rubber stocks hasbeen a serious problem for the rubber industry and one which hasreceived a great deal of attention. Problems attributable to poordispersion of sulfur in the rubber include migration of the sulfur tothe surface of the rubber stock commonly referred to as "bloom";decrease of tack at the surface of the rubber stock; variation of thephysical properties of vulcanizates from batch to batch; and others.

Compounds containing high sulfur levels can exhibit problems with sulfurbloom on the surface of the unvulcanized rubber. This surface layer ofsulfur crystallizes causing a loss of building tack which can causeproblems in tire building.

Numerous modifications of standard rubber processing techniques havebeen utilized to minimize the sulfur bloom tendencies. These priormethodologies include the use of insoluble sulfur in the compound;limiting the compound mixing temperatures during the sulfur additionstage; and minimizing the heat history that the compound is exposed toduring processing.

Insoluble sulfur is formed by rapidly quenching molten sulfur that isabove 159° C. (preferably 200° -250° C.). This product consistsprimarily of long chain sulfur molecules and a lesser amount of solubleS₈ rings. There is a tendency for the long chain molecules to revert tothe more stable soluble form if exposed to higher temperatures, longstorage times and/or hostile storage environments.

Commercial insoluble sulfur products contain a stabilizer to reduce thistendency. When insoluble sulfur is mixed in a rubber compound, it existsas more or less discreet particles of varying size in the rubber phase.Above about 118° C. sbbstantial reversion to the soluble sulfur formoccurs with resulting sulfur bloom.

An approach taken over the years has been to combine sulfur with anunconjugated diene which is believed to enhance the compatibility withthe rubber. The polymeric structure is also believed to improve thestability of the sulfur chains against breakdown to soluble S₈ units atnormal storage and processing temperatures yet readily allow the releaseof sulfur for crosslinking at vulcanizing temperatures.

U.K. Patent No. 1,232,056 discloses a method of preparing a vulcanizingagent for natural and synthetic rubbers which comprises heating togetherat a temperature of from 100°-250° C. between 3 and 50 parts by weightof sulfur and one part by weight of a conjugated diolefin in thepresence of a catalytic amount of an amine, such as adimethyl-substituted tertiary amine.

U.S. Pat. No. 2,989,513 discloses a rubber composition comprisingnatural or synthetic elastomers and from about 1 to 12% by weight basedon the weight of said rubber of a curing agent comprising at least oneinterpolymer of sulfur and an olefinic hydrocarbon selected fromstyrene, alpha-methylstyrene, butene, isobutylene, diisobutylene,triisobutylene, ethylene and propylene.

U.S. Pat. No. 3,544,492 discloses an improved curing agent which is aresinous composition formed by the reaction of one or more olefinicmaterials and a s-triazine, substituted with three groups containingactivated terminal unsaturation and sulfur.

U.S. Pat. No. 3,264,239 discloses a process and a vulcanizing agentwhich comprises preparing a mixture of sulfur, linseed oil anddicyclopentadiene, heating the resulting mixture at 125°-135° C. for atleast 5 hours to form an interpolymer, and cooling and isolating theinterpolymeric product.

U.S. Pat. No. 3,523,926 discloses a vulcanizing agent for rubbers whichis prepared by heating conjugated diolefins with sulfur in the presenceof catalytic amounts of amines.

U.S. Pat. No. 4,564,670 describes a disperse sulfur product formed bydispersing particulate sulfur in a liquid poly(cis-isoprene) dispersionagent. The product can be formed by simply mixing the liquidpoly(cis-isoprene) dispersion agent with a major amount of sulfur untilthe desired product results.

Canadian Pat. No. 965,231 claims a method for improving thedispersibility of insoluble sulfur in rubber which comprises admixinginsoluble sulfur containing up to about 70% by weight soluble sulfurwith from about 0.3 to 5% by weight based on the total weight of thesulfur of a dispersing aid selected from a specific group ofalkyl-phenoxypoly(ethyleneoxy)ethanol compounds.

Japanese Publication No. 57-133135 discloses a rubber composition withimproved sulfur bloom characterized by the addition oftriisopropanolamine, diisopropanolamine, monoisopropanaolamine or blendsthereof to a rubber composition composed of 2 to 10 weight parts ofsulfur as a vulcanizing agent blended in 100 parts of rubber selectedfrom natural rubber, synthetic rubber or rubber blended from the two.

From a review of the prior art methodologies for preparing sulfur-olefinadducts, it is quite apparent that the reaction product of sulfur and anolefin results or can result in materials that are viscous liquids orsolids. For example, U.S. Pat. No. 3,259,598 teaches that a sulfur,linseed oil, styrene reaction product can be used to vulcanize rubber.The product from this reaction mixture must be pulverized before it canbe incorporated into the elastomer due to the physical properties of thesulfur-olefin adduct.

Uniform dispersion of the sulfur in the rubber is a prerequisite foruniform vulcanization and vulcanizates with optimum mechanicalproperties and many sulfur-olefin vulcanizing compositions of the priorart require that grinding or milling steps be performed on thesulfur-olefin adduct prior to its use in rubber. This problem has beenovercome through the instant invention wherein the sulfur-olefin adductsare prepared by reacting sulfur and an olefin at 140°-160° C. withagitation in water which optionally contains a base as a catalyst and adispersing agent. The prior art does not suggest or disclose a processfor the preparation of sulfur-olefin adducts which is characterized asheating sulfur, an olefin, water, base and optionally a dispersing agentto 120°-200° C. with agitation, cooling the reaction mixture andfiltering the sulfur/olefin adduct beads.

The water serves as a medium in which the sulfur can melt and react withthe olefin in a particle form. When the reaction mixture is cooled, thesulfur/olefin adduct is frozen into a bead form. The water also acts asa heat sink for the exothermic reaction.

DISCLOSURE OF THE INVENTION

There is disclosed a novel vulcanizing agent for natural and syntheticrubbers, said vulcanizing agent is prepared by heating together withagitation at a temperature of from 120°-200° C. between 1 and 50 partsby weight of sulfur and 1 part by weight of an olefin or olefins in anaqueous reaction media in the presence of a basic catalyst and adispersing agent.

There is further disclosed a process for making a vulcanizing agentwhich comprises (1) preparing a mixture of water, sulfur and an olefinwherein from 1.0 to 50 parts by weight of sulfur per part by weight ofolefin and wherein the weight ratio of olefin plus sulfur to waterranges from 1:2.5 to 1:60, (2) heating the mixture to 120°-200° C. withagitation to form the vulcanizing agent (3) cooling the reaction mixtureand isolating the granular vulcanizing agent.

There is also disclosed a method for preparing a bloom resistantvulcanizate which comprises (1) mixing a sulfur curable rubber with from0.5 to 12% by weight of said rubber of a curing agent prepared byheating a mixture of water, sulfur and an olefin to 120°-200° C. withagitation optionally in the presence of a basic catalyst and adispersing agent; and then (2) vulcanizing the rubber/curing agentmixture.

There is also disclosed a method for preparing a rubbery vulcanizatecomprising (A) mixing a major proportion of a rubbery material havingavailable unsaturation selected from the group comprising natural andsynthetic polyisoprenes, polybutadienes, polychloroprenes, copolymers ofisobutylene and isoprene, copolymers of butadiene-1,3 and styrene,copolymers of butadiene-1,3 and acrylonitrile; with from 0.5 to 12% byweight based on the weight of said rubbery material of an adduct ofsulfur and at least one olefinic hydrocarbon selected from the groupconsisting of styrene, alpha-methylstyrene, butene-1, butene-2,isobutylene, diisobutylene, cyclooctadiene, dicyclopentadiene,cyclopentadiene and propylene; said adduct being prepared by heating amixture of water, sulfur and olefinic hydrocarbon to 120° C. to 200° C.for 1 to 3 hours with stirring; (B) vulcanizing the rubberymaterial-sulfur adduct mixture.

The rubbers useful as ingredients in the vulcanizates of this inventioninclude rubbery materials having available unsaturation such as naturaland synthetic vulcanizable rubbers and rubbery polymers of dienespreferably of open chain conjugated dienes having from 4 to 8 carbonatoms. Specific examples of rubbery materials which may benefit from thesulfur-olefin adduct of this invention are natural rubber,polybutadiene-1,3, polyisoprene, poly-2,3-dimethyl-butadiene-1,3,poly-2-chlorobutadiene-1,3 and the like. Other rubbers useful are thesynthetic rubbers such as those obtained from 1,3-dienes by means ofpolymerization or the rubbery copolymers, terpolymers and the like ofthese and similar conjugated dienes with each other or with at least onecopolymerizable monomer such as isobutylene, styrene, acrylonitrile,methylacrylate, ethylacrylate, methyl methacrylate, 4-vinyl pyridine andthe like. The polymeric diene rubbers generally contain at least 50% byweight of the diene and preferably contain from about 55-85% by weightof the diene. However, copolymers, terpolymers and other multicomponent

containing as little as 35% or less by weight of diene can also beemployed. Still other rubbery materials can be used in the practice ofthis invention such as unsaturated polymers containing acid groupsobtained by the copolymerization of a major amount of a conjugated dienewith an olefinically unsaturated carboxylic acid. Still other rubberscan be employed such as those formed by the copolymerization of dieneswith alkyl acrylates and by the polymerization of an alkyl acrylate withat least one other unsaturated monomer followed by hydrolysis. Rubberypolyesterurethanes, polyetherurethanes and polyesteramideurethaneshaving curable double bonds or available unsaturation and rubberreclaimed from the foregoing can also be used. Mixtures of two or moreof the foregoing rubbers may be employed as ingredients in thevulcaiizates of this invention. The preferred rubbers are the naturaland synthetic polyisoprenes, the polybutadienes, the polychloroprenes,the copolymers of isobutylene with isoprene, butadiene-1,3 with styrene,and butadiene-1,3 with acrylonitrile.

The novel sulfur-olefin adducts produced according to the presentinvention comprise adducts of sulfur and one or more olefinic compounds.Specific olefinic compounds which are useful in the present inventioninclude but are not limited to olefinic hydrocarbons such as ethylene,propylene, butene, isobutylene isopentene, diisobutylene,triisobutylene, hexyl-2-decene-1, and heptadecene-7; cycloalkenes suchas cyclopentene and cyclohexene; unsaturated terpenes such as pinene,camphene, and myrcene; aralkenes such as styrene, dithydronaphthalene,indene, alpha-methyl styrene and polyolefins such as butadiene,isoprene, chloroprene, cyclopentadiene, dicyclopentadiene,cyclohexadiene, vinyl cyclohexene, 1,7-octadiene, cyclooctadiene and thelike. The preferred olefinic compounds are styrene, alpha-methylstyrene, cyclopentadiene and dicyclopentadiene.

Elemental sulfur is used in preparing the sulfur-olefin adduct curingagents of this invention.

A catalyst may be employed to facilitate the formation of thesulfur-olefin adduct although they are not necessary. Representative ofthe basic materials which may be used to catalyze the formation of thesulfur-olefin adduct include calcium carbonate, sodium carbonate, sodiumhydroxide, tetramethylethylene diamine and the like.

Representative of the dispersing agents that may be used in thepreparation of the sulfur-olefin adduct include polyethylene oxides,carboxymethyl cellulose, polyvinylalcohol, and the like.

The reaction to form the sulfur-olefin adduct is advantageously andnecessarily carried out in water to accomplish the benefits of theinstant invention.

The weight ratio of water to sulfur plus olefin can vary from 2.5:1 to60:1. Preferably the ratio is 7:1 to 4:1 with 5:1 being most preferred.The weight ratio of sulfur to olefin can vary from 1:1 to 50:1, with 6:1being preferred.

The sulfur-olefin adduct curing agents of this invention are prepared attemperatures in the range of from 120° C. to 200° C. and preferably from140°-160° C. Most preferably, the reaction is conducted at least 150° C.At temperatures below 145° C., the beads after isolation willagglomerate unless a cross-linkable monomer such as divinylbenzene isused in conjunction with a peroxide in the reaction mixture. Thereaction, since it is conducted above the boiling point of water, isnecessarily conducted in a closed vessel such as an autoclave.

The vulcanizates of this invention comprise as essential ingredients amajor proportion of a single rubbery material or a mixture of two ormore rubbery materials and a minor proportion of a single or a mixtureof sulfur-olefin adduct curing agents. Other appropriate compoundingingredients such as reinforcing agents, fillers, accelerators,plasticizers, antioxidants, age resistors, resins, dyes, color pigmentsand the like may be employed with the rubbery compositions disclosedherein in the amounts customarily employed in the rubber industry.

The sulfur-olefin curing agent of this invention is useful in the rangeof from about 0.5 to about 12 parts by weight per 100 parts by weight ofthe rubbery material to be vulcanized. The preferred range is from about1 to about 5 parts by weight per 100 parts of rubbery material. Therubber stocks containing the curing agent and other appropriatecompounding ingredients can be mixed on a mill or other suitable mixingdevice such as a Banbury and the resulting blend can be cured attemperatures of from about 120° C. to about 180° C. and preferably atfrom about 130°-160° C.

The vulcanizates of the present invention are useful in tire treads,tire sidewalls, carcass stocks, V-belts, gloves, shoe heels, shoe soles,printing rollers, colored rubber articles and wherever it is desired toprovide a stable elastomer that does not exhibit sulfur bloom.

In the following illustrative examples, the amounts of ingredients aregiven in parts by weight unless otherwise specified.

PRIOR ART PROCESS Comparative Example 1 Reaction of DCPD with Sulfur

Into a 500 ml flask equipped with a temperature controller, nitrogeninlet tube and mechanical stirrer

225 g of sulfur, 75 g of dicyclopentadiene (DCPD) and 3 g of N,N,N¹,N¹-tetramethylethylene diamine (TMEDA). The flask was flushed withnitrogen and the mixture was heated to 140° C. Stirring was started whenthe sulfur had melted. The reaction exothermed to 165° C. and became tooviscous to stir in 25 minutes. The product solidified at 165° C. andupon cooling resembled concrete.

COMPARATIVE EXAMPLE 2

Into a 500 ml flask equipped with a temperature controller, nitrogeninlet tube and mechanical stirrer were placed 270 g of sulfur, 30 g ofDCPD and 0.6 g of TMEDA. The flask was flushed with nitrogen and themixture was heated to 140° C. for 45 minutes. The hot product was pouredinto an aluminum pan where it eventually solidified. The reaction flaskwas discarded because of the difficulty involved in cleaning off theproduct.

PROCESS OF THE INVENTION EXAMPLE 1

Into a one liter autoclave were placed 75 g of sulfur, 25 g of DCPD, 500ml of water, 10 g of calcium carbonate as a catalyst, and 6.5 g ofcarboxymethyl cellulose as a dispersing agent. The autoclave was flushedwith nitrogen and heated to 140° C. for three hours with stirring. Theautoclave was cooled to 13° C. and small brown beads of product werefiltered from the water. Differential scanning calorimetry showed that areaction had occurred between the sulfur and the olefin.

EXAMPLE 2

Into a 4 liter autoclave were placed 425 g of sulfur, 75 g of DCPD, 2500ml of water, 20 g of calcium carbonate as a catalyst and 32 g ofcarboxymethyl cellulose as a dispersing agent. The autoclave was flushedwith nitrogen and heated to 150° C. for three hours with stirring. Aftercooling to room temperature, small beads of brown product were filteredfrom the water. Differential scanning calorimetry indicated that areaction had occurred.

EXAMPLE 3

Into a 4 liter autoclave were placed 425 g of sulfur, 75 g ofalpha-methylstyrene, 2500 ml of water, 20 g of calcium carbonate as acatalyst and 32 g of carboxymethyl cellulose as a dispersing agent. Theautoclave was flushed with nitrogen and heated to 150° C. for threehours with stirring. After cooling to room temperature, the product wasisolated as an orange powder.

EXAMPLE 4

1.0 g of polyvinylalcohol (Vinol® 203 from Air Products) was dissolvedin 2500 ml of water. This solution was added to a 4 liter reactor with425 g of sulfur, 75 g of DCPD, and 20 g of calcium carbonate. Thereactor was sealed and heated with stirring to 150° C. for three hours.After cooling to room temperature, the small beads of sulfur/DCPD adductwere filtered.

EXAMPLE 5

Into a 4 liter autoclave were placed 425 g of sulfur, 75 g of DCPD, 2500ml of water, 20 g of calcium carbonate and 5.0 g of Igepal®-630 (GAF).The reactor was sealed and heated to 150° for three hours with stirring.After cooling to room temperature, the sulfur/DCPD adduct was isolatedas small ribbons.

EXAMPLE 6 No Dispersing Agent

Into a 4 liter autoclave were placed 425 g of sulfur, 75 g of DCPD, 2500ml of water and 20 g of calcium carbonate. The reactor was then sealedand heated to 150° C. for three hours with stirring. After cooling toambient temperature, the sulfur/DCPD adduct was isolated as small beads.

EXAMPLE 7 Peroxide and Divinylbenzene

Into a 4 liter autoclave were placed 425 g sulfur, 50 g DCPD, 20 gstyrene, 5 g divinylbenzene, 2500 ml of water, 20 g CaCo₃, 32 gcarboxymethyl cellulose and 7.1 g of a 70% solution oft-butylhydroperoxide in water. The reactor was sealed and heated to 140°C. for three hours. After cooling to ambient temperature, thesulfur/olefin adduct was isolated as beads.

EXAMPLE 8 No Catalyst

Into a 4 liter autoclave were placed 425 g sulfur, 75 g DCPD, 2500 gwater and 32 g carboxymethyl cellulose. The autoclave was sealed andheated to 150° C. for three hours with stirring. After cooling toambient temperature, the sulfur/olefin adduct was isolated as beads.

EXAMPLE 9

Into a44 liter autoclave were charged 1800 g of water, 478 g of sulfur,84 g DCPD, 36 g of carboxymethyl cellulose and 15 g of calciumcarbonate. The reactor was sealed and heated to 150° C. for 3 hours withstirring. After cooling to room temperature, beads of sulfur/olefinadduct were isolated.

EXAMPLE 10

Into a 4 liter autoclave were charged 425 g of sulfur, 75 g DCPD, 2500ml of water, 20 g of calcium carbonate and 32 g of carboxymethylcellulose. The reactor was sealed and heated to 150° C. for three hourswith stirring. After cooling to ambient temperature, the beads werefiltered.

EXAMPLE 11

Into a 4 liter autoclave were charged 425 g sulfur, 60 g of DCPD, 15 gstyrene, 2500 ml of water, 20 g of calcium carbonate and 32 g ofcarboxymethyl cellulose. The reactor was saaled and heated to 150° C.for three hours with stirring. After cooling to ambient temperature, thebeads were filtered.

The ability of the sulfur-olefin adduct prepared according to Examples10 and 11 to cure rubbers was compared with that of insoluble sulfurusing a prepared unvulcanized blend of natural and syntheticpolyisoprene rubber.

Two rubber stocks were prepared by employing the following recipe setout in Table I. All parts are parts by weight.

                  TABLE I                                                         ______________________________________                                        Component         Control  Experimental                                       ______________________________________                                        Polyisoprene/Natural Rubber (Non-productive)                                                    176.05   176.05                                             Hexamethoxy methylmelamine                                                                      2.80     2.80                                               Retarder          0.10     0.10                                               Antioxidant       0.75     0.75                                               Zinc Oxide        3.00     3.00                                               Accelerator       0.60     0.60                                               Secondary Accelerator                                                                           0.60     0.60                                               Insoluble Sulfur  3.00     0                                                  Sulfur-Olefin Adduct                                                                            0        2.83                                               from Example 10/11                                                            ______________________________________                                    

The components were mixed in a Banbury. The quantities and materialsused were those typically used in the art for producing vulcanizedrubber. The amount of sulfur-olefin adduct used was such that itsavailable sulfur was substantially equivalent in weight to the weight ofsulfur used in the control. The Banbury mix time required to incorporatethe sulfur-olefin adduct was similar to that required to incorporate theinsoluble sulfur therein.

As an additional comparative, a commercially available sulfur-olefinadduct obtained from Wyrough and Loser, Inc. known as Thio-Cure-BR wasused in place of the insoluble sulfur and the adducts from Examples 10and 11 however, at a level of 3.0 instead of 2.83.

The vulcanizable compositions were pressed out and cured in a rubberpress for about 40 minutes at 150° C. to provide cured slabs fortesting. The physical properties for the controls and the experimentalsamples are set out in Table II.

A critical factor in the utility of rubber chemicals is how well theycan be dispersed into the rubber. Clearly, if the chemicals are not welldispersed, they cannot fully take part in the cure. It has been found,through a dispersion test, that the sulfur/DCPD/styrene adduct preparedaccording to this invention is dispersed into rubber better than asulfur/DCPD adduct. The test consists of mixing the material into therubber using a Banbury, sheeting the rubber out on a mill and visuallyobserving unbroken beads in a standard size area. The dispersion valuesranged from 0-5 with 0 being complete dispersion and 5 being the poorestdispersion. The dispersion values for the controls and Examples 10 an 11in Table II were control - 0, sulfur/DCPD - 4, sulfur/DCPD/styrene - 0,Thio-Cure BR - 5. The test demonstrates that the sulfur curativesprepared according to the instant invention, when DCPD and styrene areused as the olefins, had comparable dispersion ability to insolublesulfur and much better dispersability than the commercially availableThio-Cure.

The data indicates that the sulfur-olefin adduct prepared according tothis invention had better scorch delay than the control but cured at aslower rate. In addition, the curative from Examples 10 and 11 reached amuch higher state of cure than the commercially available Thio-Cure-BR.

It was further found that the vulcanizable compositions containing thesulfur-olefin adducts prepared according to this invention had bloomresistance similar to compositions made with insoluble sulfur.

From the studies conducted on the sulfur-olefin adducts preparedaccording to this invention, it was demonstrated that elastomers curedwith the product of this invention exhibited much less bloom thanorthorhombic sulfur and equivalent bloom to insoluble sulfur.

INDUSTRIAL APPLICABILITY

The above Examples clearly demonstrate the utility of the sulfur-olefincuring agents of the present invention. These curing agents can beemployed in a wide variety of rubber stocks and the resultingvulcanizates have physical properties comparable to those achieved withconventional sulfur cure but with none of the attended disadvantagesrelated to bloom. The sulfur-olefin adduct curing agents thus offerimproved results over presently known commercial sulfur containingcuring agents.

It is, of course, to be understood that the foregoing examples areintended to be illustrative only and that numerous changes can be madein the ingredients, proportions and conditions specifically disclosedtherein without departing from the spirit of the invention as defined inthe appended claims.

What is claimed is:
 1. A process for preparing a rubbery vulcanizatecomprising: (1) mixing a major proportion of a rubbery material having aavailable unsaturation selected from the group consisting of natural andsynthetic polyisoprenes, polybutadienes, polychloroprenes, copolymers ofisobutylene and isoprene, copolymers of butadiene-1.3 and styrene andcopolymers of butadiene-1,3 and acrylonttrile with from 0.5 to about 12%by weight based on the weight of said rubbery material of an adduct ofsulfur and at least oen olefin; said adduct of sulfur and at least oneolefin is prepared according to the process comprising: (a) admixingsulfur and at least one olefin, water, a dispersing agent and a basiccatalyst wherein the weight ratio of sulfur to olefin is from 1:1 to50:1 and the weight ratio of water to sulfur plus olefin is from 2.5:1to60:1; (b) heating the mixture to 120° to 200° C. with agitation for asufficient time to form the granular vulcanizing agent; (c) cooling andisolating the granular vulcanizing agent and; (2) vulcanizing therubbery material sulfur adduct mixture.
 2. A process according to claim1 wherein the olefin is a mixture of dicyclopentadiene and styrene atratios of 2:1 to 5:1 by weight dicyclopentadiene to styrene.
 3. Aprocess according to claim 1 wherein the dispersing agent is selectedfrom the group comprising polyethylene oxides, carboxymethyl celluloses,and polyvinyl alcohols.
 4. A process according to claim 1 wherein theweight the ratio of sulfur to total olefin is from 3:1 to 10:1 and theweight ratio of water to sulfur plus olefin is from 3:1 to 7:1 andwherein the mixture is heated at a temperature of from 140° to 160° C.for from 3 to 6 hours.
 5. A process according to claim 1 wherein thebasic catalyst is calcium carbonate and wherein said basic catlayst ispresent at a weight ratio of sulfur plus olefins to calcium carbonate offrom 20:1 to 30:1 by weight.